This invention relates to a closure for round-mouthed canisters, in particular a closure having portions which are inserted into the mount of the canister and clamped therein through radial expansion of an annular wall portion or skirt of the closure.
A closure of the above kind, designed for a bottle or a like container, and comprising a skirt flexibly connected with a bottom composed of an intermediate ring panel and a central panel, is disclosed in U.S. Pat. No. 3,244,308 to Vincent J. Esposito. At the upper end of the skirt there is provided a peripheral flange which through abutment against the rim of a container sidewall defining a container opening limits the depth to which the closure is lowered into the opening. In the starting position, the bottom of the closure has a concave shape, that is to say, the bottom faces the container space to be sealed with a hollow side. For clamping the closure in the container opening, the central panel of the closure bottom is depressed through its dead center.
A disadvantage of the Esposito closure is that, in the closed position, the bottom has been pressed beyond its dead center, which means that the annular wall of the closure does not have the maximum outward diameter. The diameter of the skirt of the closure is increased because of a decrease in the absolute value of the slope of the intermediate portion. The largest diameter corresponds to no slope at all. As a consequence, the sealing effect depends to a great extent of the elasticity of the material of the closure, particularly the material of the skirt portion. In addition, a rather accurate fit in the container opening is required.
Another drawback of the Esposito closure is that movement of the closure bottom from concave to convex during closing causes a superatmospheric pressure to be generated within the container closing. Such a superatmospheric pressure, even if not arising from movement of the closure bottom but, for example, from an increase in temperature, will tend to flex the bottom back through its dead center to its concave position and thus automatically release the cover.
A further drawback of the Esposito closure is that, because of the single-wall construction, its transverse structural strength is limited. In particular, the clamping force is limited for closure of wider openings, unless thick materials are used.
U.S. Pat. No. 2,966,276 to Hing, relates to a double-walled stopper with a bottom member which is moved from a convex starting position, as viewed from the interior of the container, to a concave sealing position. As with the Esposito disclosure, the closure bottom wall is pulled through the flat configuration. There are no gradual transitions between the release position and the clamping position, and a relatively complicated central knob serves for fixing at least the concave sealing position.
German Offenlegungsschrift No. 2,425,985 to Zimmerman relates to a double-walled closure, which includes a top portion and a bottom portion in which the bottom portion includes a skirt designed for clamping against the wall of a container opening, and in which the center of the bottom portion is connected through threaded elements with the top cover. Rotation of the top portion deforms the bottom portion from a flat starting position to a concave position, viewed from the interior of the container, to thereby laterally spread the skirt of the bottom portion, which becomes wedged in the container opening. This closure of Zimmerman can only function if the bottom portion and the skirt of the bottom portion are made of elastic material, and hence the closure is only suitable for container openings having a small diameter, such as vacuum flasks.
It is an object of the invention to provide a canister closure suitable for canisters with a wide opening, in the order of 110 mm diameter, which canisters are suitable for storing foods in kitchens, such as macaroni, beans, peas, coffee, tea and the like, and which overcomes the drawbacks of the prior art to the extent that the closure is structurally strong, so that a large clamping force can be exercised even with large diameters, and the sealing range is accurately controllable within a range in which, starting from a convex position of the closure bottom portion, as viewed from the interior of the canister, the bottom curvature is varied to less convex, but the bottom never become flat or concave.
Another object of the invention is to provide such a large diameter closure which enables the user to apply the desired amount of clamping force even with dimensional variations usually experienced in canister openings.